The invention relates to a device and a method for discharging an energy storage device, in particular an intermediate circuit capacitor, in a high-voltage network, in particular a direct-current intermediate circuit in a motor vehicle.
In the case of hybrid vehicles or motor vehicles having an electric drive or a fuel cell drive, voltages are generally used that can amount to several 100 volt. Voltages that are greater than 60 volt are described in this case as “high-voltage”. For reasons of protecting life and health, it must be possible to switch off high-voltage vehicle electrical systems in motor vehicles and to discharge said systems within a predetermined time period. Known high-voltage vehicle electrical systems comprise for this purpose active and/or passive discharge devices. The high-voltage vehicle electrical system in a hybrid vehicle or a motor vehicle having an electric drive or a fuel cell drive—frequently also referred to as direct-current intermediate circuit—comprises in the simplest case an energy source in the form of a battery, a voltage converter having a direct-current intermediate current capacitor that is used as a buffer capacitor for stabilizing the operating voltage of electric consumers, one or a plurality of electric machines and further high-voltage consumers. Following a separation of the high-voltage network from the energy source, which separation can be achieved, for example, by pulling out the relevant plug connection during the course of maintenance work or also as a result of an accident, all the energy storage devices that are connected to the high-voltage network or to the direct-current intermediate circuit must be discharged (emergency rapid discharge). In so doing, it is possible for capacitors, such as an intermediate circuit capacitor, or for example also powering-down motors to function as energy storage devices. A conventional passive discharge device, i.e. a discharge device, whose function is ensured even in the event of all the supply and control lines failing, provides in so doing in the simplest case an ohmic discharge resistor that is permanently connected in parallel to the intermediate circuit capacitor.
DE 10 2007 047 713 A1 discloses a method for discharging a high-voltage network, in particular a direct-current intermediate circuit that can be connected to an energy source by means of at least one resistor, in which the at least one resistor is used as a common resistor both for charging or pre-charging and also for discharging the intermediate circuit capacitors of the direct-current intermediate circuit.
A further device known from DE 10 2008 010 978 A1 for discharging an electrical network or an electrical component, comprising a switchable resistor, provides that the switchable resistor comprises a PCT resistor and a switch that are thermally coupled and further provides that the control connection of the switch is connected to the network voltage.
A device is known from DE 10 2004 057 693 A1 for rapidly discharging a capacitor, in particular an intermediate circuit capacitor, wherein the capacitor is connected by way of an alternating-current converter to an electric motor and is connected by way of a direct-current converter to a further electric charge storage device, in particular a battery in a vehicle electrical system. In so doing, the direct-current converter comprises means that effect a rapid discharge of the capacitor whilst correspondingly controlling the direct-current converter. In particular, a resistor is connected by means of a switch to the direct-current converter on the battery side for receiving the electric power that is to be discharged.